.wrap690 {
  width: 690px;
  margin-left: auto;
  margin-right: auto;
}
.dummy_div {
  padding-bottom: 800px;
}

@media screen and (max-width: 640px){
	html {
    scroll-behavior: smooth;
  }
  .dummy_div {
    padding-bottom: 400px;
  }

	
	
	
}